RIO Ferdinand's return from suspension should bring stability to Manchester United's defence, according to official statistics from the Barclays Premiership.

The England international is available to play against Liverpool on Monday after serving an eight-month ban for failing to attend a drug test.

His last appearance was against Wolves in January when the 25-year-old was taken off injured just after half time.

Kenny Miller scored the winner for the Premiership strugglers later in the game - and it took United another two months to keep a clean sheet in Ferdinand's absence.

The Actim Index - the official player ratings system of the Barclays Premiership - gives each player a rating for how effective each performance is, showing United defenders to have underperformed compared to the start of last season.

In the opening five games of last season Ferdinand made three appearances and had an Actim Index rating of 0.58.

After five games this term, no United defenders have come close to that rating - the highest ranked player is Mikael Silvestre with 0.48.

Put into context, each player adds to his total with each game and Ferdinand only played three of the first five last term but Silvestre has featured in all five this season.

The concept of the system is to give each player a rating regardless of which position they play in. Goals, shots on target, corners, fouls, offside, passes, tackles, blocks and clearances are all analysed.

Ex-professionals report on the action live at the grounds, then a rating is generated automatically once the match statistics are fed into the mathematical programme.

The formula awards points based on each player's match contribution.

Points are based purely on performances and in theory there is no limit to a player's points-scoring potential over the season.

Thierry Henry was the most effective player last season. The Arsenal striker topped the Actim Index with a rating of 9.89 and leads this season with 1.60.

The statisticians at the University of Salford, who work in partnership with the Press Association, show United players are not playing as well as they were a year ago.

After one goal-scoring appearance Gabriel Heinze (0.26) has nearly caught up with John O'Shea's (0.29) rating with the Republic of Ireland defender playing three more games.

Despite their poor start to this season, United defenders rated fairly highly last season and three defenders were in the top 50 most effective players.

Gary Neville scored an impressive 5.19 but the England full-back is missing from the Liverpool clash, increasing the pressure on manager Sir Alex Ferguson to include Ferdinand.

Liverpool's defenders have enjoyed a more successful start to the season with Steve Finnan (0.59), Jamie Carragher (0.57) and Sami Hyypia (0.56) all scoring higher than United defenders.

However, neither side have a player in the top 10 of the Actim Index, compared to Arsenal's six.